1. Field of the Invention
The present invention relates to a laser apparatus configured to amplify pulsed seed light and output amplified pulsed laser light.
2. Related Background Art
A laser apparatus of a MOPA (Master Oscillator Power Amplifier) configuration with a seed light source and an optical amplification section is configured to amplify seed light output from the seed light source in the optical amplification section and output the amplified light.
The optical amplification section to be preferably used is, for example, a configuration including an optical fiber with a core doped with a rare earth element (e.g., Yb, Er, Nd, Tm, Ho, Tb, or the like), as an optical amplifying medium. When the rare earth-doped optical fiber is used as an optical amplifying medium, there are many advantages, e.g., easy handling because of confinement of the pump light and laser light in the optical fiber, no need for large-scale cooling equipment because of good heat radiation, and so on.
Yb (ytterbium) among the rare earth elements as a dopant in the optical fiber as an optical amplifying medium has a high conversion efficiency. For this reason, the Yb-doped optical fiber is widely used as an amplification optical fiber for high power. Like the other rare earth elements, Yb is also excited with supply of pump light and the remaining pump light not absorbed is output from the other end of the amplification optical fiber.
FIG. 5 in U.S. Pat. No. 5,867,305 discloses the configuration to inject a pulse of pump light and to make a coincidence between an end of the pulsed pump light and an end of an individual injected signal (seed light) pulse. In this configuration, individual pulses of injected signal (seed light) correspond to respective pulses of pump light. U.S. Pat. No. 5,867,305 discloses nothing about adjustment of output of the pump light at a time of switching of the seed light from pulse operation to CW operation.